3 Answers
3

Not that I know of. The closest stock solution I personally use is to take activate the utility to take a screenshot of a screen portion (Command ⌘+Shift ⇧+4). The cursor will turn into a crosshair with the screen's horizontal and vertical pixel coordinates. You then have to apply some math to determine the distance between the end-points you want to measure. Not ideal, but better than nothing.

You can also try using xScope, a nice 3rd party utility which makes life a little bit easier with dedicated tools, but it is zoom agnostic, so make sure you measure at 100% zoom.

Photoshop is the only tool that effectively takes pixel distances regardless of the zoom level, but you have to open the image or at least a screenshot (if you take it from a website or PDF) in Photoshop.

I generally use Gimp for this task, although it is indeed also ill-suited for making a quick one-off calculation.
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noffleSep 24 '12 at 22:23

While in the crosshair-selection mode, while the mouse is moving, the coordinates are the size of the screenshot. For a second or so after the mouse pauses, the coordinates show the location on the screen of the crosshair. To get the coordinates in a window or image, start the selection box at the upper-left of the window or image.
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CajunLukeSep 26 '12 at 2:39

You can do this simply by dragging from the desired pixel to the lower left corner of the screen. This will create a selection rectangle, and the size of that rectangle is shown in the screen. Since the rectangle can only stretch until it reaches the origin (the corner), its size will be the same as the pixel coordinates you're looking for.